In ancient Egypt, saws made of copper are documented as early as the Early Dynastic Period, circa 3,100–2,686 BC.[1][page needed] Examples of saws and models of saws have been found in many contexts throughout Egyptian history. Particularly useful are tomb wall illustrations of carpenters at work that show sizes and the use of different types. Egyptian saws were set with the teeth projecting only on one side, rather than in the modern fashion with the more advantageous alternating set.
According to Chinese legend, the saw was invented by Lu Ban.[2] In Greek mythology, as recounted by Ovid,[3] Talos, the nephew of Daedalus, invented the saw. In archeological reality, saws date back to prehistory and most probably evolved from Neolithic stone or bone tools. "[T]he identities of the axe, adz, chisel, and saw were clearly established more than 4,000 years ago."[4]

I tend to agree that later scavenging is more likely, even much more likely, but wouldn't completely rule out the first possibility.

At some point after those trees were cut, this stand of trees was entirely forgotten. So one way or another, it happened a long time ago.

Presumably there are some clues elsewhere in the area. I'm thinking buildings, carvings, furniture etc. made with the scavenged wood, whether extant or buried/ruined. If they were cut less than, say, 500 years ago I'd expect it to be possible (which is not to say easy) to find some of the wood still in use somewhere.

Doesn't have to be a cross-cut saw. There were also rope and chain (non-powered, natch) saws. Cannot give a provenance, and I note there is very little evidence of such tool usage, and the study of this new site is on-going.

not at all. i assume the stump top was pointy like the rest and maybe slightly above the muck, and was exposed say circa 1940s, and someone with no sense of archaeology went out to deal with a navigation hazard.

it just does not look like something cut thousands of years back, nor with a rope saw.

I'm trying to formulate some joke about what Ken Ham could learn about trees being submerged underwater for over a year, but it just makes me sad. He'd find something to reaffirm his preferred narrative.

OK, as @rupertj already pointed out we have a headline problem - "visible for the first time in centuries" is just not true. So, whether the reason was navigation or not I'm now pretty well convinced any such cuts are relatively recent.

Edit: at 9:44 of the video linked by rupertj, you'll see a scientist's saw half way through a trunk. I don't think it's the same trunk in the photo posted here, or even in the same stand of stumps, but it's irrefutable proof of recent sawing.

I have only skimmed this study from 1938, but it doesn't seem to mention the cuts: